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Design Search Autocomplete (Google / YouTube Suggest)

HLD

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Live AI Interview

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USection 01Design Search Autocomplete (Google / YouTube Suggest)

Problem Understanding

Restate the problem in your own words.

What this step looks like in a real interview: Before you draw a single box, demonstrate that you understand the system you're designing. Read the problem statement and example products at the top of this section, then write what the system is, who uses it, and the headline scale + UX expectations — in your own words. Strong candidates anchor the rest of the interview by getting the framing right here.

ProblemWhat you're designing

Design Search Autocomplete (Google / YouTube Suggest)

Asked atGoogle· L5Amazon· SDE3Meta· E5

Design a typeahead / search-autocomplete service: as the user types each character, return the top 5–10 matching completions (queries, products, places) ranked by frequency or relevance, with sub-100 ms latency at keystroke-level QPS (every keystroke is a query). The hard parts are the trie / inverted-index data structure, frequency updates as queries flow in, regional + personalised ranking, and absorbing spikes during news events when one query dominates the head.

Real-world examples

Google Search autocomplete
The canonical example — personalised, regional, language-aware completions ranked by frequency + recency.
Amazon search
Product autocomplete with inventory + relevance signals; conversion-tuned, not pure-frequency.
YouTube search
Title + topic autocomplete on top of a 100M+ video catalog with trending boosts.
Algolia
Hosted typeahead used by thousands of e-commerce sites; sub-50 ms p99 globally.

Your task: read the problem above, then write what the system is, who uses it, the rough scale, and the headline UX expectation — in your own words. Submit for AI review when you're ready.

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Your understanding

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